Wall Covering

a material, primarily paper-based, used for the decoration of interior spaces; it usually comes in rolls.

Wallpaper was for a long time the traditional wall covering in such Eastern Asian countries as Japan and China. Wall coverings made of cloth, such as damask, were used exclusively in Europe until the 18th century to cover both walls and ceilings. With the development of the paper industry, cloth wall coverings were replaced by wallpaper, which was less expensive. Wallpaper may be plain or patterned and of one or several colors. At the present time, wall covers are increasingly being manufactured from polymers.

There are three principal types of wall coverings: conventional wallpaper, washable wall coverings, and sound-absorbent wall coverings (napped). Conventional wallpaper may be unprimed (the pattern is applied directly on white or colored paper) or primed (the pattern is applied to a precolored paper surface). It may be patternless, in a single flat color. Some wallpaper is embossed, with a pattern in relief.

Washable wall coverings may be printed with colors having a water-resistant polymer additive. Some are printed and then covered with a protective coating of polymer emulsions and varnishes. Washable wallpapers may have a thin polymer color coating, which is subsequently embossed. Some wall coverings are essentially opaque polymer films with a printed pattern. Washable wall coverings, which can withstand repeated washings with warm water and soap, are noted for their high wear resistance.

Sound-absorbent wallpapers are covered by any one of various napped fibrous materials (primarily textile waste). A vacuum cleaner is used to clean the surface of such wall coverings.

Wall coverings, in addition to being decorative, are important for reasons of health, since they cover small holes and cracks in walls. Their color also has an effect on the lighting in a room.

Manufacture. The production of hand-printed wallpaper on an industrial basis began in Great Britain in the 18th century. The printing process was mechanized in the 1820’s, after the invention of the paper machine, which made it possible to manufacture various lengths of paper.

Wallpaper production consists of the following processes: preparing the color components, priming the paper, printing the pattern, finishing (embossing, glossing, surface coating and, in some cases, applying an adhesive layer to the back), rewinding, sorting, and packaging.

The preparation of the color components includes selecting the colors; preparing the binder, emulsions, and varnishes; and mixing the components.

The paper is primed by a coating machine, which consists of a roll-unwinding device, a color applicator, a drying section, and a winder for rolling up the coated paper. Coating machines are distinguished according to the type of color applicator used. Thus, there are roller or brush coating machines and machines with a flexible or air doctor blade.

The print is applied by special printing machines, which operate in a manner similar to that of the coating machines. The printing machines vary in their printing procedure and in their capacity for printing plates. Coating and printing machines are further classified according to the type of drying method that they use. Festoon-drying and chamber types are most commonly used.

Three printing methods are currently used: letterpress, gravure, and silk-screen. The cylinders used for letterpress printing have a length corresponding to the width of the wallpaper to be produced and a diameter ranging from 95 to 185 mm. The diameter is determined by the pattern. Hardwood (pear, walnut, maple, and apple) and pressed-paper cylinders are used. A type of letterpress printing also used is flexography, in which the printing plates are made from an elastic material. The plates for gravure are also cylinders, but the pattern is incised in the plate rather than raised.

The silk-screen method involves a tightly stretched screen, through which the coloring matter is forced onto the paper. The area of the screen outside the desired pattern is coated with varnish so that an impression of the pattern remains on the base after the coloring matter is pressed through with a doctor blade. A modification of this method is the rotary silk-screen process, which permits a continuous printing process. The printing element in the process is a seamless tube, or sleeve, with a thin, perforated wall on which the coloring matter is applied, as in the flat-bed silk-screen process. Within the sleeve is mounted a doctor blade, which presses the coloring paste through the mesh onto the web pressed against the screen—that is, onto the base for the wall covering.

The desired properties and artistic effect of a wall covering are rendered by using certain types of raw materials (hydrophobic binders, fast dyes, different types of bases) and different finishing techniques (embossing; film coating; relief application of coloring matter, plastisols, fibers, and threads; application of an adhesive to the back).

The final stage in the production of wall coverings involves rewinding the material onto rolls of appropriate length, sorting according to grade and color, labeling, packaging, and storing. The rewinding process is performed mechanically on automatic and semiautomatic machines.

There has been a trend in the wallpaper industry to combine production processes, to increase paper widths by two or three times, and to adopt automated process-control and quality-control systems. New printing methods are being introduced, as are new chemical processes for the production of new raw materials.